1. Field of the Invention
This invention relates to a carrier apparatus for carrying a plane member such as a semiconductor wafer, a mask for manufacturing semiconductor devices, an optical disk substrate, a liquid crystal panel and so on.
2. Description of the Related Art
There are many demands for carrying a flat member precisely. One of these demands appears in the semiconductor field.
X-ray lithography systems have been developed as a lithography system to produce ultra large scale integrated circuits (ULSI). The X-ray lithography systems use X-ray from syncrotron orbital radiation (SOR) as an exposure light. By this kind of X-ray lithography, fine circuit patterns of a width is not more than 0.2 .mu.m can be transferred to semiconductor wafers.
A conventional structure of such an X-ray lithography system is shown in FIG. 1.
Referring FIG. 1, on a wafer stage frame 11, a wafer table 13 is installed. The wafer table 13 comprises four stages. The stages have six degrees of freedum which are the X-direction, Y-direction, Z-direction, .theta.x-rotation, .theta.y-rotation and .theta.z-rotation respectively. In front of the wafer table 13, a wafer chuck plate 17, which can hold and release a plane member such as a semiconductor wafer 15 by vacuum absorbing, is attached. On the other hand, a mask 19 in which described circuit patterns are attached is connected to a mask frame 23 with a mask chuck plate 21. The mask 19 is placed against the semiconductor wafer 15 holding by the mask chuck plate 21.
Then, the position of the semiconductor wafer 15 is adjusted and fixed in X-, Y-, Z-direction, .theta.x-,.theta.y- and .theta.z-rotation by the four stages. The circuit patterns in the mask 19 are transferred on the semiconductor wafer 15 by exposure of X-ray emission from SOR.
Between the wafer stage frame 11 and the mask frame 23, a wafer carrier apparatus 25 is installed. The wafer carrier apparatus 25 carries the semiconductor wafer 15 and sets up the wafer 15 to the wafer chuck plate 17 or removes the wafer 15 from the wafer chuck plate 17 The wafer carrier apparatus 25 comprises a carrier arm 27 which extends vertically to the position where the semiconductor wafer 15 is fixed, a Z-direction loader 29 which moves the carrier arm in the Z-direction with a moving means such as a motor or an air cylinder device, a X-direction loader 3 which moves the carrier arm in the X-direction (perpendicular to paper) with a moving means such as a motor or an air cylinder device, and a rail 33 which guides the X-direction loader 31 when the loader 31 moves in X-direction.
FIG. 2 and FIG. 3 show how to hold the semiconductor wafer 15 to the wafer chuck plate 17.
A holding part 41, which can hold and release the semiconductor wafer 15 at the back side of the wafer, is formed on the top end of the carrier arm 27. In the holding part 41 a vacuum chucking cavity 43 is shaped. To the vacuum chucking cavity 43, a vacuum suction pipe 45 is joined. On the other hand, in the chucking face 17a of the wafer chuck plate 17, a vacuum chucking cavity 47 is shaped annularly. To the vacuum chucking cavity 47 a vacuum suction pipe 49 is joined.
The semiconductor wafer 15 is chucked and held on the holding part 41 of the carrier arm 27 and carried in the Z-direction by the Z-direction loader 31 from a starting position to the chucking point in front of the wafer chuck plate 17. After that, the semiconductor wafer 15 is carried on the Z-direction loader 29, then chucked and held on the chucking face 17a of the wafer chuck plate 17.
In the lower part on the surface of the wafer chuck plate 17, it has a notch 51 into which the holding part 41 of the carrier ar 27 is able to enter and deliver the semiconductor wafer 15 to contact with the wafer chuck plate 17 closely.
However, in the case of the conventional apparatus as described above, the carrier arm 27 is united to the holding part 41 directly in one body. Therefore, when the semiconductor wafer 15 is handed over to the wafer chuck plate 17, if the degree of parallelization between the semiconductor 15 and wafer chuck plate 17 is not enough to properly hand the wafer 15 over, as shown in FIG. 3, a space S results between them and the chucking power often can not be generated. The semiconductor wafer 15 might fall from the wafer chuck plate 17 depending on circumstances.
When the semiconductor wafer 15 is carried to a horizontal wafer chuck, the position of the semiconductor wafer 15 with respect to the wafer chuck plate 17 might vary because of insufficient holding power by wafer chuck plate 17.
The unstable position problem such as is described above occurs in the case of a mask held with a mask chuck and also in the case of flat members held to semi-conductor apparatus such as a testing apparatus, eching apparatus, CVD (Chemical Vapor Deposition) apparatus and so on.